Polyester resins are synthetic resins which are polycondensation products prepared by the reaction of dicarboxylic acids with dihydroxy alcohols. Unsaturated polyester resin compositions contain ethylenic unsaturation, usually introduced by unsaturated diols and acids or both, either alone or in combination with saturated diols and acids. Unsaturated polyester resins are cross linked with a compatible monomer, such as a styrene monomer or an acrylic monomer, in amounts ranging from 0% to 50% by weight, thus providing in the presence of a catalyst, like a peroxide, a cured polyester thermosetting resin. Unsaturated polyester resins are prepared typically by maleic and fumaric acids, which may include saturated acids, such as phthalic and adipic acids, and which unsaturated acids may be acid anhydrides. Generally, the dihydroxy alcohols are ethylene, propylene, diethylene and dipropylene glycols. Cross linking agents are typically a styrene monomer and diallyl phthalate.
Unsaturated polyester resin compositions have long been used to prepare composite laminate-type structures. Such laminate structures have often employed a lightweight core material, such as balsa wood, cut or sprayed rigid polyurethane foam and PVC foams, as the core material to produce such composite structures. Generally, an unsaturated resin composition is applied to one or both surfaces of the lightweight core material over a gel coating layer, typically containing pigments to form a top surface of a composite laminate structure. The rigid polyurethane foams employed in such core materials have been cut to dimensions; however, rigid polyurethane foams have also been applied as a spray to the backing layer of an unsaturated polyester resin on the gelcoat layer to form a composite laminate.
Polyurethane products are produced by the condensation reaction of a polyisocyanate, such as a diisocyanate, and a hydroxyl-containing material, such as a polyol, to provide both flexible and rigid polyurethane foam having densities varying from about two to thirty pounds per cubic feet. Rigid polyurethane foams used as core materials are prepared by employing a polyether, such as a polypropylene glycol reacted with a diisocyanate in the presence of water as a blowing agent, and a catalyst (amines, such as a polyethanol polyamine, like diethanol tetramine, and metal salts, such as tin compounds, like dialkyl tin), so that the water reacts with the diisocyanate to cause cross linking and also produce carbon dioxide which produces a polyurethane rigid foam material. Other blowing agents may be employed, such as fluoro hydrocarbons or hydrocarbons and other volatile materials. Generally, rigid polyurethane foams are based on polyethers made from sorbitol, methyl glucoside, sucrose, or combinations thereof. Rigid polyurethane foams are employed for forming lightweight, rigid composite structures, particularly where an unsaturated polyester resin composition is employed as a top or bottom layer with the rigid polyurethane foam material.
The preparation of composite structures using a core material and unsaturated polyester resin layers with core materials, particularly polyurethane rigid foams, share a common problem in that no chemical bond occurs between the core material and the cured unsaturated polyester resin layer composition in contact with the core material creating a structural weakness in the composite laminate product.
It is desirable therefore to provide for a new and improved polyurethane foam composition which may be employed with unsaturated polyester resin compositions, particularly where the polyurethane rigid foam compositions form a core material in a composite, lightweight structural laminate, and wherein an unsaturated polyester resin composition is employed as one or more layers on the core material, and the cured polyester resin layer forms a strong and effective bond with the foam core material.
The invention concerns a foamable polyurethane composition suitable for use in preparing a core material in a laminate for bonding with an unsaturated polyester resin composition and to the method of preparing a hybrid, structurally rigid polyurethane-unsaturated polyester resin composite structure and the product so prepared.
The invention comprises a foamable polyurethane composition for the preparation of rigid foam polyurethane and adapted for use in bonding to an unsaturated polyester resin composition, typically employed as an unsaturated polyester resin layer in contact with at least one surface of the rigid foam polyurethane composition. The foamable polyurethane composition comprises: a) polyol b) a catalyst, for example, a gelling catalyst and a blowing catalyst, to carry out the polyurethane reaction; c) a blowing agent to provide a rigid polyurethane foam; and d) a polyisocyanate, such as MDI or prepolymer or diisocyanate to react with the polyol with the polyisocyanate generally being in a stoichiometric amount or in a slight excess.
The polyurethane composition also includes or has added thereto an additive organic compound having an active hydroxyl group which reacts with the polyisocyanate and which also contains an available, unreacted ethylenically unsaturated group which reacts subsequently with the monomer-containing unsaturated polyester resin composition applied to the rigid polyurethane foam, thereby providing a strong chemical bond between the rigid polyurethane foam and the cured unsaturated polyester resin composition layer. The additive compound comprises from about 1% to 20% by weight of the polyisocyanate of the polyurethane composition. The ethylenically unsaturated group of the foamable polyurethane composite is available for reaction with the monomer in the unsaturated polyester resin, so that on curing of the unsaturated polyester resin layer, such as by the use of organic peroxide, blown with or without the use of metal salt promoters and accelerators, a strong chemical bond is formed between the rigid polyurethane foam core material, typically as an inner core section of a composite laminate, and the cured unsaturated polyester resin layer.
The additive may be a prepolymer having free isocyanate groups and prepared by reacting said additive organic compound with said active hydroxyl group with separately a polyisocyanate or said polyisocyanate to form a prepolymer, the prepolymer having an unreacted, ethylenically unsaturated group after the reaction with the polyisocyanate to react with a peroxide-curable monomer-containing unsaturated polyester resin composition.
The polyols useful in the polyurethane compositions are selected to provide for a rigid or semirigid polyurethane foam and typically would be a polyol, such as a polyether polyol made from sorbitol, methyl glucoside, or sucrose, a glycerine polyol and hydroxyl amines, and combinations thereof. Aromatic polyesters useful in the polyurethane composition generally comprise saturated aromatic polyesters, for example, prepared by the reaction of phthalic acid, like an dialkyl (i.e. dimethyl) terephthalic acid, with a polyol, such as a polyalkylene glycol, like diethylene or dipropylene glycol, or a terephthalate-ethylene glycol polyester polyol, to provide the aromatic polyester polyol. The polyurethane composition may contain combinations of the polyether polyols and the saturated phthalic-polyol esters. The blowing agent in the polyurethane composition typically and preferred is water; however, other blowing agents, such as fluorocarbon blowing agents, such as chlorocarbon blowing agents, may also be employed, as well as other volatile hydrocarbons. The catalyst employed in the polyurethane composition constitutes a wide variety of catalysts which accelerate the polyurethane reaction including amines, metal carboxylates, particularly tin soaps and organic tin compounds, alone and in combination, used in a catalytic amount, e.g. of 0.01% to 2.0% by weight.
The polyisocyanate generally comprises a diisocyanate, either aliphatic or aromatic, and particularly is MDI or an MDI prepolymer in a stoichiometric amount or in a slight stoichiometric excess, such as up to five percent, relative to the polyether polyol or aromatic polyester. The composition may also include, alone or with the diisocyanates, isocyanate prepolymers, such as a uretonomine polymer and polymeric isocyanates. The diisocyanates used usually have a functionality of greater than two and generally have at least two free isocyanate (NCO) groups ranging from 28% to 33% by weight. In addition, the polyurethane and the polyester compositions may comprise and include various additives, such as polyols or other catalysts, like a gelling catalyst and a blowing agent catalyst, accelerators, flame retardants, but not limited to, such as halo-alkyl phosphates, like polychloro alkyl phosphates, re-enforcing additives, inorganic and fiber fillers, stabilizers, surfactants, such as silicones, and the like, alone or in various combinations. Generally, the polyurethane compositions are divided into an A side and a B side which on mixing, such as at a spray nozzle, are reacted to form a polyurethane foam, with the A side comprising the polyisocyanate, such as the MDI or prepolymer and the organic additive, while the B side comprises the polyol or polyether and the catalyst and various additives. The polyurethane composition may include up to 50% by weight of glass fibers.
The additive organic compound employed may be added to either the A or B side or separately introduced prior to reaction, but generally is added to the A side with the polyisocyanate either reacted with the polyisocyanate in the A side or added as a prior-reacted MDI additive compound. The additive organic compound is selected to have an active hydrogen functionality, such as at least one active hydroxy group, which will enter into a reaction with the polyisocyanate separately or during the polyurethane foam reaction. It also includes one or more ethylenically unsaturated groups (e.g., allyl or acrylic) which do not enter into the urethane reaction, and which are then available for cross linking with the monomer employed in the unsaturated polyester resin composition. Some organic compounds suitable for use in the invention and reaction with the diisocyanate comprise allyl alcohol alkanoates, and more particularly, allyl alcohol ethyoxlate or propoxylated, hydroxy polyester acrylates and polypentaerythritols, e.g. triacrylate and ethyoxylated and propoxylated trimethylol propane poly(tri)acrylates, and combinations thereof.
The organic additive compounds can be added to the B side polyol components of the polyurethane composition, whereby on addition of the B side to the A side, an in situ reaction occurs to form the organic additive compounds.
The polyurethane composition may comprise an A side wherein the polyisocyanate comprises a diisocyanate and includes the additive organic compound or prepolymer, and a B side which comprises the polyether polyol or polyester polyol, the catalyst and the blowing agent; or may comprise an A side wherein the polyisocyanate comprises a diisocyanate and a B side which comprises the polyether polyol or polyester polyol, the catalyst, the blowing agent and the additive organic compound or prepolymer.
The polyester resin compositions employed in the invention are employed to provide one or more cured resin layers in contact with the foam polyurethane either provided in cut form or spray form, and used to form one or more layers of an inner core material of a laminate structure. The polyester resin layer forming a thin, cured, thermosetting layer on one or both sides and generally one side having a gel layer of a cured unsaturated polyester resin composition which contains pigments, such as titanium dioxide, which provides for a hard, cured, white top surface layer. The unsaturated polyester resin composition may contain up to 50% of a monomer, styrene or acrylic monomer, and generally up to about 30% by weight of the styrene monomer, and includes promoter salts therein, so that on the addition of an organic peroxide, the polyester resin cures.
The promoted (containing metal salt) one or more unsaturated polyester resin composition may be sprayed as barrier coats behind and on top of a gelcoat with a very fast cure time with rapid cure to reduce the styrene monomer loss. The employment of a barrier coat, typically with about 5% to 20% of fiberglass sprayed therewith, strengthens the gelcoat, reduces water absorption and lowers water and vapor transmission, particularly where the polyester resin contains an acrylic urethane oligomer therein. Thus, in the preparation of the hybrid foam polyester structural laminates of the invention, a standard, general purpose, promoted unsaturated polyester resin composition may be employed and cured by adding, for example, 0.5% to 2% by weight an organic peroxide, like methyl ethyl ketone peroxide, but usually also employing a cobalt carboxylate, such as cobalt octoate, or other fatty acid cobalt salt.
The hybrid-polyester polyurethane structural foam laminates comprise an inner core structure formed of the rigid polyurethane foam, and which foam contains the unreacted, ethylenically unsaturated groups from the organic additive compound. An unsaturated, promoted polyester resin composition is applied to at least one surface of the rigid polyurethane foam, such as by coating or spraying, and the thickness of which surface may vary, but generally is less than the thickness of the inner core layer, or example, may range from 5 millimeters to 200 millimeters, and more typically, 50 to 150 millimeters. The layer is generally applied with a reinforcing filler additive, either particulate material, or more particularly, glass fibers, ranging from about 0% to 50% by weight, e.g. 5% to 30%, in order to provide strength to the structural foam laminate. The unsaturated polyester resin composition is applied over a thin gelcoat, which gelcoat would form the top or finish surface of the foam laminate and can be comprised of a cured unsaturated polyester resin composition, and usually contains fillers or pigments or combinations, such as metal oxides, like titanium dioxide, to add a white color to the surface of the foam laminate. The gelcoat layer would range from about 5 mils to 50 mils, and more typically, from 20 mils to 35 mils.
The hybrid composite structure typically has a gelcoat layer which ranges from about 1 mil to 20 mils in thickness, the cured polyester layer ranges from about 50 mils to 200 mils in thickness, and the rigid polyurethane foam core layer ranges from about 200 mils to 1000 mils in thickness.
For a composite structural foam laminate employing rigid polyurethane foam as a core material which is used together with a layer of unsaturated polyester resin composition over a gelcoat, it has been found that the cured polyester resin composition layer sprayed on top of the rigid polyurethane foam may be removed with little difficulty and without the sign of any chemical adhesion, and thus constitutes a very weak bond and has no chemical bond between the cured unsaturated polyester resin composition and the basic core material. However, with the employment of an organic additive with and in the formation of the rigid polyurethane foam, the unreacted double bonds allow the unsaturated polyester resins and the monomer therein, in reaction, to react chemically with the unreacted double bonds of the rigid polyurethane foam, thereby creating a strong chemical bond between the cured polyester resin layer and the rigid polyurethane foam layer.
The invention includes the method of preparing a rigid polyurethane foam for use as a core material in a composite structure, which method comprises: preparing a foam polyurethane composition consisting essentially of an A side comprising a polyisocyanate to react with a polyether polyol or aromatic polyester polyol, and a B side consisting essentially of a polyether polyol or aromatic polyester polyol, a catalyst and a blowing agent; adding to the A side or the B side an additive organic compound or a prepolymer prepared by the reaction of the additive organic compound with a polyisocyanate and having free isocyanate groups having an active hydroxyl group to react with the polyisocyanate on the A side, and having after the reaction an available unreacted ethylenically unsaturated group to react with a peroxide-curable, promoted, monomer-containing unsaturated polyester resin composition; and reacting the A and B sides together to form a rigid polyurethane foam. The method includes spraying the A and B sides of the polyurethane foam composition in the presence of glass fibers to form a rigid polyurethane foam-containing glass fibers therein, and wherein the glass fibers comprise about 1% to 50% by weight of the rigid polyurethane foam.
The invention will be described for the purposes of illustration only in connection with certain embodiments; however, it is recognized that those persons skilled in the art may make various modifications, changes, additions and improvements to the illustrated embodiment, all falling within the spirit and scope of the invention.
A conventional, sprayable, structural polyurethane foam composition was prepared as follows:
100 parts of MDI (Papi-94 from Dow Chemical Company) a 2.3 functionality 32 NCO % diisocyanate.